The present invention relates to a dry etching method for a material containing silicon, a method for fabricating a semiconductor device using the dry etching method, and a dry etching apparatus for implementing the dry etching method.
When dry etching is performed with respect to a material containing silicon (hereinafter referred to as the silicon-containing material) in the fabrication of a semiconductor device, a dry etching apparatus having a dual power source such as an inductively coupled plasma etching apparatus (ICP) has been used to miniaturize a semiconductor element and increase the precision thereof. The dry etching apparatus having the dual power source features separate and controlled application of first electric power (hereinafter referred to as source power) for generating a plasma of a process gas introduced into a chamber and adjusting the density of the plasma and second electric power (hereinafter referred to as bias power) for drawing ions (etching species) from the plasma into an object to be etched. The use of the dry etching apparatus having the dual power source provides high-accuracy processing properties. In a typical dry etching apparatus having a dual power source, the source power is applied to a coil or the like provided on an outer wall of the chamber and the bias power is applied to a sample stage provided in the chamber to carry the object to be etched.
The step of forming an isolation in a silicon substrate has conventionally used LOCOS (Local Oxidization of Silicon) for forming the isolation by locally oxidizing the silicon substrate masked with a nitride film. As feature sizes have been reduced increasingly, however, the problem has arisen that the isolation is larger than a desired size, which makes it difficult to provide an active region having a sufficient size. To solve the problem, STI (Shallow Trench Isolation) has been used as a replacement in which an isolation is formed by forming a trench in a silicon substrate, filling an oxide film in the trench, and then planarizing a surface of the silicon substrate including a surface of the oxide film by CMP (Chemical Mechanical Polishing). The foregoing dry etching apparatus having the dual power source is used to form the trench for isolation.
Herein below, a conventional method for fabricating a semiconductor device, specifically a method for forming a trench for isolation by etching a silicon substrate by using the dry etching apparatus having the dual power source will be described with reference to the drawings.
FIGS. 11A to 11D are cross-sectional views illustrating the individual process steps of the conventional method for fabricating a semiconductor device.
First, as shown in FIG. 11A, a first silicon oxide film 81 is formed on a silicon substrate 80 by thermal oxidation, followed by a silicon nitride film 82 formed on the first silicon oxide film 81 by using a film forming method such as CVD (chemical vapor deposition). Then, a resist pattern 83 having openings each corresponding to a region to be formed with an isolation is formed on the silicon nitride film 82 by photolithography.
Next, as shown in FIG. 11B, dry etching is performed with respect to the silicon nitride film 82 and to the first silicon oxide film 81 by using the resist pattern 83 as a mask, thereby patterning each of the silicon nitride film 82 and the first silicon oxide film 81. Thereafter, the resist pattern 83 is removed by ashing and the silicon substrate 80 is cleaned.
Next, as shown in FIG. 11C, dry etching is performed with respect to the silicon substrate 80 by using the patterned silicon nitride film 82 as a mask, thereby forming trenches 84 for isolation in the silicon substrate 80. A detailed description will be given to the dry etching step shown in FIG. 11C. First, the silicon substrate 80 as an object to be etched is placed in the chamber (not shown) of the dry etching apparatus. Then, the chamber is evacuated till a specified degree of vacuum is reached and a gas required to etch the silicon substrate 80 (hereinafter referred to as a process gas), specifically a mixture of a halogen-containing gas such as Cl2 or HBr and an oxygen gas is introduced into the chamber. Subsequently, a plasma of the process gas is generated by initiating the application of source gas and then ions in the plasma are drawn into the silicon substrate 80 by initiating the application of bias power. As a result, the ions in the plasma and an exposed portion of the silicon substrate 80 react with each other to form a volatile reaction product (such as a compound of silicon and chlorine). At this stage, dry etching is performed with respect to the silicon substrate 80 by evacuating the chamber and thereby exhausting the foregoing volatile reaction product from the chamber. Thereafter, the silicon substrate 80 is cleaned such that a deposit (such as a compound of the foregoing volatile reaction product and oxygen) formed on the silicon substrate 80 during dry etching is removed therefrom, whereby the trenches 84 are formed in the silicon substrate 80.
Since the dry etching step shown in FIG. 11C requires processing accuracy as high as required by the processing of a gate electrode due to a reduced size of the isolation, a dry etching apparatus having a dual power source such as an inductively coupled plasma etching apparatus is used in the dry etching step.
Next, the portions of the silicon substrate 80 located adjacent the wall and bottom surfaces of the trench 84 are thermally oxidized by using an oxidation furnace in order to lower a surface state in the portions of the silicon substrate 80. Then, a second silicon oxide film 85 is deposited on the silicon nitride film 82 by CVD to completely fill the trench 84. Subsequently, a surface of the silicon nitride film 82 including a surface of the second silicon oxide film 85 is planarized by CMP such that the portions of the second silicon oxide film 85 located externally of the trenches 84 are removed. Thereafter, the silicon nitride film 82 is removed by wet etching and the first silicon oxide film 81 remaining on the surface of the silicon substrate 80 is removed by cleaning the silicon substrate 80 as shown in FIG. 11D, whereby isolations composed of the second silicon oxide film 85 filled in the trenches 84 are formed.
A description will be given herein below to a conventional method of applying the source power and the bias power in the dry etching step using the dry etching apparatus having the dual power source and shown in FIG. 11C (hereinafter referred to as the conventional dry etching method) and to the effect of the conventional dry etching method.
FIG. 12 shows an example of the respective time-varying effective values of the source power and the bias power in the conventional dry etching method. In FIG. 12, the time at which the application of the source power is initiated is used as the reference for power application time (0 second). In the present specification, the effective value of the bias power is the effective value of the bias power actually applied to the sample stage and the effective value of the source power is the effective value of the source power actually applied to the coil or the like. The effective value is defined herein as the value of an alternating power equal to the square root of the arithmetic mean of the squares of the instantaneous values taken throughout one complete cycle.
As shown in FIG. 12, the application of the bias power is initiated one second after the application of the source power is initiated. On the other hand, the effective value of the source power is set to 600 W, while the effective value of the bias power is set to 200 W.
FIGS. 13A to 13C are views showing the effect of the conventional dry etching method, specifically showing changes in the internal state of the chamber of the dry etching apparatus in the dry etching step shown in FIG. 1C, of which FIG. 11A shows the state immediately after the introduction of the process gas into the chamber, FIG. 11B shows the state immediately after the application of the source power is initiated, and FIG. 11C shows the state immediately after the application of the bias power is initiated. It is to be noted that the silicon nitride film and the like on the silicon substrate as well as the sample stage and the like in the chamber are not depicted in FIGS. 13A to 13C.
First, as shown in FIG. 13A, the silicon substrate 80 as an object to be etched is placed in a chamber 86 of the dry etching apparatus. Then, the chamber 86 is evacuated till a specified degree of vacuum is reached and a process gas 87 required to etch the silicon substrate 80 is introduced into the chamber 86. Then, as shown in FIG. 13B, a plasma 87A of the process gas 87 is generated with application of the source gas. Thereafter, ions 88 in the plasma 87A are drawn into the silicon substrate 80 with application of the bias power, as shown in FIG. 13C.
Thus, the dry etching apparatus having the dual power source is capable of controlling the generation of the plasma of the process gas and the adjustment of the plasma density independently of the drawing of the ions from the plasma into the object to be etched. In accordance with the conventional dry etching method using the dry etching apparatus having the dual power source, therefore, etching is performed with respect to the object to be etched by generating the plasma of the process gas with application of the source power and then drawing the ions from the plasma into the object to be etched with application of the bias power.
If a trench for isolation is formed in a silicon substrate by using the conventional dry etching method, e.g., however, etching is halted halfway, as shown in FIG. 14, which leads to the problem that the trench for isolation having a desired isolation depth cannot be formed. FIG. 14 shows the state in which etching has been halted halfway in the dry etching step shown in FIG. 11C. In FIG. 14, the same reference numerals as used in FIG. 11C are retained for the same members.
If the conventional dry etching method is used for a silicon substrate or the like as an object to be etched, an etching-induced damaged layer is formed in the silicon substrate or the like, which causes the problem that the electric characteristics of the semiconductor device are degraded.
If a trench for isolation is formed in a silicon substrate by using the conventional dry etching method, e.g., it is necessary to thermally oxide the portions of the silicon substrate located adjacent the wall and bottom surfaces of the trench for isolation in order to lower a surface state in the portions of the silicon substrate, while cost for fabricating the semiconductor device is increased disadvantageously by using an oxidation furnace.
In view of the foregoing, it is therefore a first object of the present invention to prevent a halfway halt in etching performed with respect to a silicon-containing material by using an etching apparatus having a dual power source. A second object of the present invention is to prevent the degradation of the electric characteristics of a semiconductor device induced by a damaged layer formed in the silicon-containing material during dry etching. A third object of the present invention is to lower a surface state in the portions of the silicon substrate located adjacent the wall and bottom surfaces of a trench for isolation at low cost.
To attain the first object, the present inventors have examined the cause of an etching halt in the conventional dry etching method (see FIG. 14) and found the following fact.
FIGS. 15A to 15C are views illustrating the mechanism of the etching halt occurring in the conventional dry etching method, specifically showing the internal states of the chamber of a dry etching apparatus at different times in the dry etching step shown in FIG. 11C, of which FIG. 15A shows the state immediately after the application of the source power is initiated in the chamber in which a process gas has been introduced, FIG. 15B shows the state in which the application of the source power is continued before the application of the bias power is initiated, and FIG. 15C shows the state immediately after the application of the bias power is initiated. It is to be noted that a silicon nitride film and the like on a silicon substrate as well as a sample stage and the like in the chamber are not depicted in FIGS. 15A to 15C.
First, as shown in FIG. 15A, the silicon substrate 80 as an object to be etched is placed in the chamber 86 of the dry etching apparatus. Then, the chamber 86 is evacuated till a specified degree of vacuum is reached. Subsequently, the process gas 87 (such as a mixture of a halogen-containing gas and an oxygen gas) required to etch the silicon substrate 80 is introduced into the chamber 86 and the source power is applied, whereby the plasma 87A of the process gas 87 is generated.
Next, if the application of the source power is continued before the application of the bias power is initiated, active oxygen (hereinafter referred to as oxygen radicals) 89 is generated in conjunction with the ions 88 as an etching species in the plasma 87A, as shown in FIG. 15B. At this time, the oxygen radicals 89 and an exposed portion of the silicon substrate 80 react with each other to form a thin silicon oxide film 90 on the silicon substrate 80.
Next, as shown in FIG. 15C, the ions 88 in the plasma 87 are drawn into the silicon substrate 80 with application of the bias power. However, since the silicon oxide film 90 has been formed on the silicon substrate 80 as an object to be etched and an etching speed for the silicon oxide film is about one hundredth of an etching speed for silicon, etching performed with respect to the silicon substrate 80 hardly proceeds.
To verify the mechanism of the etching halt in the conventional dry etching method (FIGS. 15A to 15C), the present inventors conducted the following two experiments.
First, to verify oxidization at a surface of the silicon substrate when the application of the source power is continued before the application of the bias power is initiated in the first experiment, the thickness of the silicon oxide film formed on the surface of the silicon substrate was measured by exposing the silicon substrate to the plasma generated only with application of the source power for a specified period. At this time, an inductively coupled plasma etching apparatus was used as a dry etching apparatus having a dual power source and the respective effective values of the source power and the bias power were set to 600 W and 0 W. As a process gas, a mixture of Cl2 and O2 gases (Pressure: 7 Pa, Cl2 Gas Flow Rate: 150 ml/min, O2 Gas Flow Rate: 6 ml/min) was used.
FIG. 16 shows the result of the first experiment, specifically the dependence of the thickness of the oxide film (the vertical axis) at the surface of the silicon substrate on the source power application period (the horizontal axis).
As shown in FIG. 16, it was found that, if the application of the source power was initiated before the application of the bias power was initiated, oxidization at the surface of the silicon substrate proceeds with a lapse of the source power application period to form a thick oxide.
Next, to verify the relationship between each of the timing of applying the source power and the timing of applying the bias power and a halt in etching performed with respect to the silicon substrate in the second experiment, the etching depth (hereinafter referred to as an amount of shaved silicon) was measured when dry etching was performed with respect to the silicon substrate, while varying the timing of initiating the application of the source power and the timing of initiating the application of the bias power. As a sample used in the second embodiment, a silicon substrate formed by the conventional method for fabricating a semiconductor device shown in FIGS. 11A and 11B (the silicon substrate 80 formed with the silicon nitride film 82 as a mask pattern for forming isolation) was selected.
An objective value of the amount of shaved silicon was set to 300 nm in the second experiment. As a dry etching apparatus having a dual power source, an inductively coupled plasma etching apparatus was used and the respective effective values of the source power and the bias power were set to 600 W and 200 W. As a process gas, a mixture of Cl2 and O2 gases (Pressure: 7 Pa, Cl2 Gas Flow Rate: 150 ml/min, O2 Gas Flow Rate: 6 ml/min) was used.
In the second embodiment, the time at which the application of the source power was initiated was used as the reference time and the time at which the application of the bias power was initiated was expressed as a delay time from the reference time (which assumes a negative value if the time at which the application of the bias power was initiated precedes the time at which the application of the source power was initiated).
FIG. 17 shows the result of the second experiment, specifically shows the dependence of the amount of shaved silicon (the vertical axis) on the delay time (the horizontal axis).
As shown in FIG. 17, it was found that a halt in etching performed with respect to the silicon substrate occurred if the application of the source power was initiated before the application of the bias power was initiated. Specifically, even if an interval between the time at which the plasma is generated with application of the source power and the time at which the application of the bias power is initiated, i.e., an interval between the time at which the application of the source power is initiated and the time at which etching of the silicon substrate is initiated is short, oxidization proceeds at the surface of the silicon substrate and etching performed with respect to the silicon substrate is halted consequently.
From the results shown in FIGS. 16 and 17, the present inventors have concluded that, to attain the first object, i.e., to prevent a halfway halt in dry etching performed with respect to the silicon-containing material, it is important to prevent oxidization at a surface of the silicon-containing material during dry etching. As a specific method for preventing oxidization at the surface of the silicon-containing material, the present inventors have developed a method of initiating the application of the bias power before initiating the application of the source power in the dry etching apparatus having the dual power source. As a value predetermined for an effective value of applied power is larger, the time required by the effective value to reach the predetermined value from the initiation of the application thereof becomes longer. Even in the case where a value predetermined for the effective value of the source power (second predetermined value) is higher than a value predetermined for the effective value of the bias power (first predetermined value) and where the application of the source power is initiated at the same time as or before the application of the bias power is initiated, if the effective value of the source power reaches the second predetermined value after the effective value of the bias power reaches the first predetermined value, effects equal to those achieved by the foregoing xe2x80x9cmethod of initiating the application of the bias power before initiating the application of the source powerxe2x80x9d are achievable.
The present inventors have also found that, if etching is performed with respect to the silicon-containing material by using the dry etching apparatus having the dual power source, the second object can be attained, i.e., the degradation of the electric characteristics of the semiconductor device can be prevented by applying the source power by continuously using the same dry etching apparatus having the dual power source as used for etching without applying the bias power, thereby oxidizing the damaged layer formed in the silicon-containing material during etching and then removing the oxidized damaged layer by cleaning the substrate.
Further, the present inventors have found that the third object can be attained, i.e., a surface state in the portions of the silicon substrate located adjacent the wall and bottom surfaces of the trench for isolation can be lowered at low cost without using an oxidation furnace by applying the source power in the dry etching apparatus having the dual power source without applying the bias power and thereby oxidizing the portions of the silicon substrate located adjacent the wall and bottom surfaces of the trench for isolation.
The present invention has been achieved based on the foregoing findings. Specifically, to attain the first object, a dry etching method according to the present invention assumes a dry etching method using a dry etching apparatus having a dual power source capable of independently controlling source power for generating a plasma in a chamber and bias power for drawing ions from the plasma into an object to be etched in the chamber, the method comprising the steps of: placing a substrate having a member containing at least silicon exposed thereat in the chamber; introducing a process gas containing at least oxygen into the chamber in which the substrate has been placed; and performing etching with respect to the member by generating a plasma of the process gas with application of the source power and drawing the ions from the plasma into the member with application of the bias power, the step of performing etching with respect to the member including the step of initiating the application of the bias power before oxidization proceeds at a surface of the member.
If etching is performed with respect to the silicon-containing material as the object to be etched by using the dry etching apparatus having the dual power source, the dry etching method of the present invention initiates the application of the bias power before the oxidization at the surface of the silicon-containing material proceeds. This prevents the situation in which the drawing of the ions from the plasma into the silicon-containing material is inhibited by an oxide film formed on the surface of the silicon-containing material and surely prevents a halfway halt in dry etching performed with respect to the silicon-containing material.
In the dry etching method of the present invention, the step of performing etching with respect to the member preferably includes the step of initiating the application of the bias power before initiating the application of the source power.
The arrangement ensures the drawing of the ions from the plasma into the silicon-containing material before the surface of the silicon-containing material is oxidized by oxygen radicals generated in the plasma with application of the source power and thereby ensures etching performed with respect to the silicon-containing material.
In the dry etching method of the present invention, the step of performing etching with respect to the member preferably includes the step of applying the source power and the bias power such that an effective value of the source power reaches a second predetermined value after an effective value of the bias power reaches a first predetermined value.
The arrangement ensures the drawing of the ions from the plasma into the silicon-containing material before the surface of the silicon-containing material is oxidized by oxygen radicals generated in the plasma with application of the source power and thereby ensures etching performed with respect to the silicon-containing material. Specifically, if the second predetermined value for the source power is higher than the first predetermined value for the bias power, the time at which the effective value of the source power reaches the second predetermined value is posterior to the time at which the effective value of the bias power reaches the first predetermined value even when the application of the source power is initiated at the same time as or before the application of the bias power is initiated. In this case, therefore, the same effect as achieved when the application of the source power is initiated after the application of the bias power is initiated is achievable.
In the dry etching method of the present invention, a silicon substrate, a polysilicon film, an amorphous silicon film, a silicide film, or the like may be used as a silicon-containing material.
To attain the first object, a first method for fabricating a semiconductor device according to the present invention assumes a method for fabricating a semiconductor device using a dry etching apparatus having a dual power source capable of independently controlling source power for generating a plasma in a chamber and bias power for drawing ions from the plasma into an object to be etched in the chamber, the method comprising the steps of: forming a mask pattern having an opening corresponding to a region to be formed with an isolation on a silicon substrate; placing the silicon substrate formed with the mask pattern in the chamber; introducing a process gas containing at least oxygen into the chamber in which the silicon substrate has been placed; and forming a trench for isolation in the silicon substrate by generating a plasma of the process gas with application of the source power, drawing ions from the plasma into the silicon substrate with application of the bias power, and thereby performing etching with respect to the silicon substrate, the step of forming the trench for isolation including the step of initiating the application of the bias power before oxidization proceeds at an exposed portion of the silicon substrate.
If the trench for isolation is formed by performing etching with respect to the silicon substrate by using the dry etching apparatus having the dual power source, the first method for fabricating a semiconductor device initiates the application of the bias power before oxidization proceeds at the exposed portion of the silicon substrate. This prevents the situation in which the drawing of the ions from the plasma into the silicon substrate is inhibited by an oxide film formed on the surface of the silicon substrate and surely prevents a halfway halt in dry etching performed with respect to the silicon substrate. Accordingly, there can be formed the trench for isolation having a desired isolation depth in the silicon substrate.
In the first method for fabricating a semiconductor device, the step of forming the trench for isolation preferably includes the step of initiating the application of the bias power before initiating the application of the source power.
The arrangement ensures the drawing of the ions from the plasma into the silicon substrate before the surface of the silicon substrate is oxidized by oxygen radicals generated in the plasma with the application of the source power and thereby ensures etching performed with respect to the silicon substrate.
In the first method for fabricating a semiconductor device, the step of forming a trench for isolation preferably includes the step of applying the source power and the bias power such that an effective value of the source power reaches a second predetermined value after an effective value of the bias power reaches a first predetermined value.
The arrangement ensures the drawing of the ions from the plasma into the silicon substrate before the surface of the silicon substrate is oxidized by oxygen radicals in the plasma generated with the application of the source power and thereby ensures etching performed with respect to the silicon substrate.
To attain the first object, a second method for fabricating a semiconductor device according to the present invention assumes a method for fabricating a semiconductor device using a dry etching apparatus having a dual power source capable of independently controlling source power for generating a plasma in a chamber and bias power for drawing ions from the plasma into an object to be etched in the chamber, the method comprising the steps of: forming a conductive film containing at least silicon on a substrate; forming a mask pattern covering a region to be formed with a gate electrode on the conductive film; placing the substrate formed with the conductive film and with the mask pattern in the chamber; introducing a process gas containing at least oxygen into the chamber in which the substrate has been placed; and forming a gate electrode composed of the conductive film by generating a plasma of the process gas with application of the source power, drawing ions from the plasma into the conductive film with application of the bias power, and thereby performing etching with respect to the conductive film, the step of forming the gate electrode including the step of initiating the application of the bias power before oxidization proceeds at an exposed portion of the conductive film.
If the gate electrode is formed by performing etching with respect to the silicon-containing conductive film formed on the substrate by using the dry etching apparatus having the dual power source, the second method for fabricating the semiconductor device initiates the application of the bias power before oxidization proceeds at the exposed portion of the silicon-containing conductive film. This prevents the situation in which the drawing of the ions from the plasma into the silicon-containing conductive film is inhibited by the oxide film formed on the surface of the silicon-containing conductive film and surely prevents a halfway halt in dry etching performed with respect to the silicon-containing conductive film. Accordingly, there can be formed the gate electrode having a desired size.
In the second method for fabricating a semiconductor device, the step of forming the gate electrode preferably includes the step of initiating the application of the bias power before initiating the application of the source power.
The arrangement ensures the drawing of the ions from the plasma into the silicon-containing conductive film before a surface of the silicon-containing conductive film is oxidized by oxygen radicals generated in the plasma with the application of the source power and thereby ensures etching performed with respect to the silicon-containing conductive film.
In the second method for fabricating a semiconductor device, the step of forming the gate electrode preferably includes the step of applying the source power and the bias power such that an effective value of the source power reaches a second predetermined value after an effective value of the bias power reaches a first predetermined value.
The arrangement ensures the drawing of the ions from the plasma into the silicon-containing conductive film before a surface of the silicon-containing conductive film is oxidized by oxygen radicals generated in the plasma with the application of the source power and thereby ensures etching performed with respect to the silicon-containing conductive film.
In the second method for fabricating a semiconductor device, a polysilicon film, an amorphous silicon film, a silicide film, or the like may be used as a silicon-containing conductive film.
To attain the second object, a third method for fabricating a semiconductor device assumes a method for fabricating a semiconductor device by using a dry etching apparatus having a dual power source capable of independently controlling source power for generating a plasma in a chamber and bias power for drawing ions from the plasma into an object to be etched in the chamber, the method comprising the steps of: performing etching with respect to the member by placing a substrate having a member containing at least silicon exposed thereat in the chamber, introducing a first process gas into the chamber, generating a first plasma of the first process gas with application of the source power, and drawing ions from the first plasma into the member with application of the bias power; exhausting the first process gas from the chamber after the step of performing etching with respect to the member and then introducing a second process gas containing at least oxygen into the chamber, while leaving the substrate in the chamber; oxidizing a damaged layer formed in the member in the step of performing etching with respect to the member by generating a second plasma of the second process gas by applying the source power without applying the bias power; and removing the oxidized damaged layer by retrieving the substrate from the chamber and cleaning the substrate.
The third method for fabricating a semiconductor device performs etching with respect to the silicon-containing material by using the dry etching apparatus having the dual power source, oxidizes the damaged layer formed in the silicon-containing material during dry etching by applying the source power without applying the bias power by using the same dry etching apparatus having the dual power source, and then removes the oxidized damaged layer by cleaning the substrate. This prevents the degradation of the electric characteristics of the semiconductor device induced by the damaged layer formed in the silicon-containing material during dry etching. Since the damaged layer can be oxidized by using the dry etching apparatus having the dual power source used for dry etching instead of using an oxidation furnace, the fabrication cost for the semiconductor device can be reduced significantly.
In the third method for fabricating a semiconductor device, the member is preferably a silicon substrate, the step of performing etching with respect to the member preferably includes the step of forming a trench for isolation in the silicon substrate, and the step of oxidizing the damaged layer preferably includes the step of oxidizing the damaged layer formed in portions of the silicon substrate located adjacent wall and bottom surfaces of the trench for isolation.
When the trench for isolation is formed by performing dry etching with respect to the silicon substrate, the arrangement allows low-cost removal of the damaged layer formed in the portions of the silicon substrate located adjacent the wall and bottom surfaces of the trench for isolation.
In the third method for fabricating a semiconductor device, the member is preferably a conductive film formed on the substrate and containing at least silicon, the step of performing etching with respect to the member preferably includes the step of forming a gate electrode composed of the conductive film on the substrate, and the step of oxidizing the damaged layer preferably includes the step of oxidizing the damaged layer formed in a side surface of the gate electrode.
When the gate electrode is formed by performing dry etching with respect to the silicon-containing conductive film formed on the substrate, the arrangement allows low-cost removal of the damaged layer formed in the side surface of the gate electrode.
In this case, a polysilicon film, an amorphous silicon film, a silicide film, or the like may be used as a silicon-containing conductive film.
To attain the third object, a fourth method for fabricating a semiconductor device according to the present invention assumes a method for fabricating a semiconductor device by using a dry etching apparatus having a dual power source capable of independently controlling source power for generating a plasma in a chamber and bias power for drawing ions from the plasma into an object to be etched in the chamber, the method comprising the steps of: placing a silicon substrate formed with a trench for isolation in the chamber; introducing a process gas containing at least oxygen into the chamber in which the silicon substrate has been placed; forming a silicon oxide film by generating a plasma of the process gas by applying the source power without applying the bias power and thereby oxidizing portions of the silicon substrate located adjacent wall and bottom surfaces of the trench for isolation; and forming an isolation by retrieving the substrate from the chamber and filling an insulating film in the trench for isolation formed with the silicon oxide film.
The fourth method for fabricating a semiconductor device oxidizes the portions of the silicon substrate located adjacent the wall and bottom surfaces of the trench for isolation by applying the source power without applying the bias power by using the dry etching apparatus having the dual power source and thereby forms the silicon oxide film. As a result, a surface state in the portions of the silicon substrate located adjacent the wall and bottom surfaces of the trench for isolation can be reduced without using an oxidation furnace. In addition, the breakdown voltage of the isolation can be increased by rounding up the corner portions of the trench for isolation. This achieves a significant reduction in the fabrication cost for the semiconductor device. Moreover, the fourth method for fabricating a semiconductor device allows simultaneous oxidization for removing the damaged layer with oxidization for lowering the surface state and increasing the breakdown voltage by more deeply oxidizing the portions of the silicon substrate located adjacent the wall and bottom surfaces of the trench for isolation than the damaged layer formed during dry etching. In this case, the cleaning step for removing the oxidized damaged layer can be omitted.
The step of forming the isolation of the fourth method for fabricating a semiconductor device may include the step of forming the insulating film on the silicon substrate such that the trench for isolation is completely filled with the insulating film, planarizing a surface of the silicon substrate including a surface of the insulating film by CMP, and thereby removing a portion of the insulating film located externally of the trench for isolation.
To attain the first object, a dry etching apparatus according to the present invention assumes a dry etching apparatus having a dual power source capable of independently controlling source power for generating a plasma in a chamber and bias power for drawing ions from the plasma into an object to be etched in the chamber, the apparatus comprising: bias power applying means for initializing and operating a timer at the same time as application of the bias power is initiated; and source power applying means for initiating application of the source power when an elapsed time measured by the timer reaches a specified time.
In the dry etching apparatus of the present invention, the source power applying means initiates the application of the source power when the time elapsed from the time at which the bias power applying means initiates the application of the bias power reaches the specified time. In short, the application of the bias power is inevitably initiated before the application of the source power is initiated. Even if etching is performed with respect to the silicon-containing material as the object to be etched by using a process gas containing oxygen, therefore, the ions in the plasma can surely be drawn into the silicon-containing material by initiating the application of the bias power before the silicon-containing material is oxidized by oxygen radicals generated in the plasma with the application of the source power. This prevents the situation in which the drawing of the ions from the plasma into the silicon-containing material is inhibited by an oxide film formed on a surface of the silicon-containing material and surely prevents a halfway halt in dry etching performed with respect to the silicon-containing material.